This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. NLSL is a non linear least squares program for fitting CW spectra based on microscopically order but macroscopically disorder (MOMD) model. A service request was received from Mr. Francis Qufei Li for help on using our NLSL program to analyze his ESR data from a site directed spin labeled protein. The spectra were found to be in the slow motional region and consist of multiple components.